Question for NISCOPE_VAL_VOLTAGE_HIGH calculation

[kkwong]

Hi,

     When I tried to follow the description in help to check the Voltage High and Lo using the measurment  NISCOPE_VAL_VOLTAGE_HIGH and NISCOPE_VAL_VOLTAGE_LO, I found that the Voltage High returned by niscope is different from my result. But, the voltage low is the same.    Please see the attached file for details.  (PS. I built the histogram in excels not using the niscope function).

"The last histogram method is used where the voltage high result is the voltage of the histogram bin with the maximum number of hits above 60% of the waveform's voltage peak-to-peak value. This calculation is useful for ignoring the overshoot and preshoot on square waves."

Digitizer results

VHigh=3.304283  VLow=-0.030522

VHigh=3.307144  VLow=-0.055748

My results

VHigh=3.322406  VLow=-0.030522

VHigh=3.324843 VLow=-0.055748

Is my computation correct? Or is it a bug?  Niscope version is 3.5.  PXI-5224. 

[kkwong]

Hi, Just a correction, the model is PXI-5124.

[John_P1]

Hi kkwong,

From the looks of it, the Scope measurement is returning the bin immediately below the one that you are calculating in Excel.  I am not immediately sure of the cause of the discrepancy, but will keep you posted as I look into the matter further.  Thanks for posting!

 

-John 

Message Edited by John P on 04-20-2009 11:55 AM

[kkwong]

Hi John,

     Thank you for your prompt reply.  I just found that the results mismatch is due to the wrong bin frequency I defined in excel.   Here is the explanation: 

Assuming dv=Vpp/256

In the previous xls

      the bin frequencies (bin array) were calculated as Vmin+(i-0.5)*dv where i is the bin number from 0 to 255.

The bin count is for the range Vmin+(i-1-0.5)*dv  to Vmin+(i-0.5)*dv.

 The corrected xls

      the bin frequencies (bin array) should be calculated as Vmin+(i)*dv where i is the bin number from 0 to 255.

The bin count is for the range Vmin+(i-1)*dv  to Vmin+(i)*dv.

The report voltage should be Vmin+(i-0.5)*dv 

With the corrected xls, the excel and digitizer results are the same now.